feat: add portal page with application grid and settings navigation

[PawiX25]

Summary

Replaces the placeholder root page (/) with a proper portal that shows authenticated users their available applications and links to account settings.

Changes

Backend — server/src/routes/api/applications.rs

• New GET /api/applications endpoint behind require_auth middleware
• Returns applications filtered by the user's group membership (allowed_groups empty = visible to all, non-empty = user must belong to at least one group)
• Returns minimal UserApplication { name, slug, icon } response

Frontend — apps/frontend/app/page.tsx

• Unauthenticated users → redirect to /login
• Authenticated users → portal with:
  • Welcome header with display name, email, and sign out button
  • Application grid (cards with icon or initial letter fallback)
  • "Account Settings" card linking to /dashboard
  • Empty state placeholder when no applications are available
• Fade-in animation via motion/react

API Schema — packages/api-schema/api.d.ts

• Added UserApplication schema and get_my_applications operation types

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Self-Review Checklist:

• I've split up large pieces of code into smaller, reusable pieces
• No logic is duplicated that could be abstracted into a function, method, hook or middleware
• I've commented my code where needed and avoided comments that provide no value

Frontend checklist

• I've checked my code for duplicate components or UI elements that already exist elsewhere in the codebase
• Data fetching and mutations use React Query
• Forms use useForm — N/A (no forms in this PR)
• I've formatted my code using Prettier

Backend checklist

• Logic is not reimplemented manually when a suitable crate already exists
• I've used the validator crate for API input validation — N/A (no user input in this endpoint)
• I've formatted my code using rustfmt
• My code produces no new warnings with Clippy enabled

[TymekV]

The Account Settings button feels off. You could do a dropdown menu in the place of the Sign out button with options to sign out or view settings.

Or alternatively, you could try doing something similar to Authentik:

[TymekV]

Remove types that can be inferred.

Suggested change

	let user_groups: Vec<ObjectId> = user.map(|u| u.groups).unwrap_or_default();
	let user_groups = user.map(|u| u.groups).unwrap_or_default();

[TymekV]

Same here

Suggested change

	.collection::<Application>("applications")
	.collection("applications")